US2773916A - Production of 1, 3, 5-ethyl xylene, metaxylene and benzene from c8 aromatics with hf-bf3 - Google Patents

Description

States Patent y Y( McCalay, Chicago,-'Ill., assigno'rs to Standard Oil Company,- Chicago, Ill., a corporation of Indiana Application september' 26, 1952,v ser'irNo. 311,621 10 Claims. (curo-668i.,

This invention relates to the conversion of Cs aromatic components of a hydrocarbon charging stock consisting chiey of mixed xyl'enes and ethyl benzene substantially entirely into"1,3,5rethyl Axylen'e, meta-xylene 4and benzene. errployedV hereinV the expression l, 3,5'ethyl xylene is employed to denote 1,3-dirnethyl '`ethyl benzene.

' An object of the invention is to provide such a conversion process vin which by-product formation willbe subs ta'ntially eliminated. A further object is to'provide ka process in which the three desired productsvv will be obtainedV in relatively pure form. A particular object is to avoid the' presence of diethyl and triethyl benzenes in the ultimate product obtained. important object is toiefect the desired conversion at expense and with maximum eciency. Other objects will be apparent as the detailed description of the invention proceeds.

The charging stock should'cons'ist chiefly of'Cs aromatic components and shouldv be as free from C7 and C9 aromatics as is economically feasible,'the 'C9 and heavier aromatics preferably constituting less than 5% of the total charge. The charge should be substantially free from' olelins and the amount of-parains should be as low as iseconornicallyy feasible although about 10% or more ofparains may ybe tolerated. Of the Ca aromatics the niaj'o'r compohentshould'be xylene'and the minorcoinpo'- nent ethyl-benzene, the xylene to ethyl benzene ratio being in the range of 1.6:1 to 5:1 or more (including any recycled materials as a: part of the charge). While it is preferred that meta-Xylene be the major component f thexylene mixture, any mixture of orthol, lmeta'- and parax'yleiiesmay be employed.

The defined" charging stock is dried and complexed with` aboutv 6to l2 mols yof HF and about one mol of B F3 based on its aromatic content in a complexing zone which is preferably at about to 30 C; under a pressureof yaboutV A20` to 50 p. s. i. g. wherein the defined amounts of charging stock, HF and BFa are intimately mixed and contacted for a period of about 5 orl0 vminutes to forni a substantially homogeneous complexphase dissolved in which phase may containy s ome dissolved but uncomplexed hydrocarbons such as parains, which term as used herein includes naphthenes. The resulting complex stream is then pumped to a pressure of at least 20() to 300 p. s. i. g. and heated to a temperature of about 65 C., i. e. inthe range of 50? to 70 C., the pressure being higher than the HF vapor pressure after the heating step so .that liquid phase conditions will be insured. The complex is next passed through a reactor (in which stirring or contacting means is usually unnecessary) at said temperature Vand pressure wherein it is contacted in substantially' homo- "ice geneous phase for a period of .4 to 4 ltourss e. gaboiit V2 hour, during which time the following reactions occur: Ortho-xylene-Smeta-xylene Para-xylenemeta-xylene Ethyl benzene-l-meta-xylene benzene+ 1,3,5 -ethyl xylene 2 ethyl benzene-ebenzene-idiethyl benzene ((11%) Ethyl toluene-l-meta-xylenevetoluene-l-1,3,5-ethyl xylene Propyl-benzene-l-meta-xylene benzene-'i-1,3,5propyl xylene After Vabout one-half hour contact time in the reactor suflicient HF and BFs are dashed from the products to leave about 6 mols of HF and about l mol of BFs per mol of Cs and heavier aromatic hydrocarbons contained in the product stream, most of which will be in the form of HF-BFa complexes. These complexes are next washed with an inert wash liquid which boils outside of the boiling range of desired products and which is preferably` a light parafnic or naphthenic hydrocarbon such as pentane to Aremove from the complex solution paraiiinic impurities introduced with the charging stock and the benzene and toluene produced in the reactor which are not in com; plexed form. The removal of vbenzene and toluene fat this point prevents undesired reactions in a later evaporating step. Pentanemis distilled from the wash liquid =`and recycled and the hydrocarbons recovered by the pentane wash are fractionated to give substantially pure vbenzene and heavier hydrocarbon fractions containing toluene and C9 paran-iris.

The -washed complex solution which contains dissolved pentane is next introduced into an evaporator at about Vatmospheric pressure to remove additional BFa, HF and pentane, the latter being condensed, separated -and returned -to the washtower if its presence in the reactor would result in formation 'cfa separate phase. When suflicient BFs` is liberated in the evaporator, dialkylbenzenes suchv as meta-xylene (and diethyl benzene f if present) are released from their complex form an'ddissolved in remaining complex soliiticir To insure the absence of diethyl benzene in the 1,3,5-ethyl xylene product, the vxyl'enes-to-ethyl;benzene molA ratio in Ythe Ycharge should be relatively high, preferably greater than 3:1. When Athis mol ratiois substantially lower than about 3 1,y the Ydesired 1,3,5-ethyl xylene product. purity may be `attained yby washing liberatedV dialkyl-benzenesy from the liquid stream leaving the evaporator and recycling suicient dialkyl benzen'es thus obtained so that the effective charging stock will have a xylene:ethyl benzene ratio 'of about 3:1 or more. The remaining liquid from the evaporator is stripped at reduced pressure todecom'pseanfy remaining complex `and to remove as much'la's possible of theremaining HFl and -BPs for recycle. The stripped hydrocarbons may, then be neutralized Aand fractionated to givegubstantially pure -meta-xylene fand substantially pure 1,3,5-ethyl xylene. i

The accompanying drawing.'l which forms a part of the specication is aschernaticow diagram of a commercial plant which can be useddfor processing for examplesy about 2,000: barrels per d ay of a charging stockand Aproducing therefrom about 490 barrelsjper day-,of-benzeneabgut 64. Stripper 64 is yprovided with 4a reboiler orothenheating means 65 and it is operated at as low a pressure as is economically feasible, usually in the range of to 200 mm. absolute and with a bottom temperature in the range of 100 to 150 C. The HF and BFa vapors .from

stripper 64 are passed through vline 66 by compressor 67 to line 47.

The hydrocarbons released from I-IF and BFa in stripper 64 are withdrawn through line 68 by pump 69 which introduces them into neutralization system 70. The stream withdrawn through line 68 may containas much as .01% HF-BFa and hence may require caustic scrubbing or more drastic neutralization treatment than is given to the stream withdrawn from pentane stripper 33. The neutralization may be eected by well known means and hence requires no detailed description.

The neutralized stream is then introduced by line 71 to meta-xylene vfractionator 72 which is provided with a reboiler or heating means 73 at its base. Tower 72 is a schematic representation of a fractionation system that may require three towers in actual practice, but since no invention is involved in the Yfractionation system it will not be described in detail. 99% purity is withdrawn through line 74 in amounts of about 584 barrels per day. A lighter -mesitylene stream is withdrawn through line 75 in relatively small amount. The desired 1,3,5-ethyl xylene of high purity is withdrawn through line 76 in amounts of about 635 barrels per day. Any 1,3,5-propyl xylene and other bottoms materials are Withdrawn through line 77. Thus the three desired products, benzene, meta-xylene and 1,3,5-ethyl xylene, eachin a state of high purity, are recovered in a total amount of about 95% or more of the total Cs aromatics in vthe original charge.

The HF and BFs from lines 26 and 47 is `partially c ondensed in cooler 78 and separated into gaseous and liquid components respectively in separator 79. The liquid component separates into an HF phase and .a Pentane phase. The HF phase is passed by pump 80 through cooler S1 and line 16 to complex-forming vessel 12. The gaseous component, chiey BFa, is passed by compressor 82 through cooler 83 and line 17 to complexf orming vessel 12. Make up HF is introduced as required from' source 84 and make up BFa is similarly supplied from source 85. The separated pentane phase is returned .by line 86 and pump 87 to wash tower 29 or 51 when its presen ce in vessel 12 and reactor 22 would result in formation of substantial amounts of a separate paranic hydrocarbon phase. When the charge is sutliciently free from parans, the pentane may be recycled With HF to vessel 12, but it is important to have a substantially -homogeneous phase in reactor 22 and hence the parains and/ or naphthenes introduced thereto must be held within close limits, i. e. must not greatly exceed about 10%. For a completely homogeneous phase, the amount of parains present should be less than 1%.

As another example of the invention the hereinabove defined process may be applied to a charging-stock containing on a volume basis 1.3% toluene, 31.2% ethyl benzene, 6.5% paraxylene, 44.4% meta-xylene, 5.6% ortho-xylene and 11% parains with substantially no C9 ;aromatics; from about 1,600 barrels per day of such a charging stock, about 500 barrels per day of substantially ethyl benzene. If, the charge composition, -HF-BFs pro- ,l ,portions and/.or operating conditions aremodied to such anfextent that the 1,3,5-ethyl xylene. product -is contamif Meta-xylene of at least about nated by undue amounts of diethyl benzene an alternative .procedure maybe utilized to prevent ,such contamination.

complex (the latter two being of substantially equal stability). Thus in evaporator 45 sucient HF and BFa .may be removed to liberate all meta-xylene and ethyl `benzene and to leave the 1,3,5-ethyl xylene in complex form. In such a case the total liquid leaving evaporator 4 5 may be washed with a light parafnic hydrocarbon lin wash tower 51 and additional HF may be introduced .to insure that the 1,3,5-ethyl xylene complex remains in solution in the -HF phase. In this case thewashed complex can then be introduced into HF-BF3 stripper 64 vfor -releasing the 1,3,5-ethyl xylene and if all of the meta-xylene has previously been removed the 1,3,5-ethyl xylene may simply be distilled from heavier hydrocarbons. After removing the wash liquid from the liberated meta-xylene and diethyl benzene the net product meta-xylene may be distilled from the diethyl benzene and the latter, rwithout neutralization or purification but -with the amount of meta-xylene desired for recycle, may be recycled to complex-forming vessel 12. The recycled diethyl benzene is thus ultimately converted entirely to benzene and 1,3,5- ethyl xylene. In this case the meta-xylene which is separated from diethyl benzene by distillation may require neutralization and/ or treating to remove residual amounts of -HF and BFs but it should require no further fractionation or purification.

For increasing 1,3,5-ethy1 xylene production, ethylene can be added to line 19 or directly to the base of reactor 22 for alkylating meta-xylene to 1,3,5-ethyl xylene in addition to reactions previously set forth. The ethyleneis added after the complexing step in vessel 18 because with HF alone, fully alkylated tetraethyl xylene would be formed whereas the introduction of ethylene into the complex solution in or entering reactor 22 results almost exclusively in 1,3,5-ethyl xylene. The amount of ethylene so introduced must be so limited that the mol percent of xylenes in thereactor eluent will exceed the mol per- Vcent of ethyl xylene, the ethylene introduced to the re,

actor corresponding on a mol basis to increasing the amount of ethyl benzene in the original charge.

From the foregoing description of particular examples it will be apparent that the objects of the invention have been attained. It should be understood, however, that the invention is not limited to the detailsrecited in these examples since alternative procedural steps and operating conditions will be apparent from the above description to those skilled in the art.

We claim:

1. A process for converting the Cs aromatic components of a hydrocarbon charging stock consisting chiefly of mixed xylenes and ethyl benzene substantially entirely into benzene, meta-xylene yand l, lil-dimethyl, S-ethyl benzene which process comprises complexing the aromatic components of said charging stock in substantially dry state with at least about 6 mols of HF and 1 mol of BFS per mol of total aromatic hydrocarbon in the charge in a complexing zone, increasing the pressure and temperature on the complexes thus formed and holding complexes at a temperature in the range of about 50 C. to about C. under a pressure of at least 200 p. sfi. g. and

high enough to insure liquid phase conditions long enough aromatic hydrocarbons contained in the product stream,

4thereafter removing.. uncomplexed hydrocarbons from the complexes by washing said .complexes countercurrently with a saturated hydrocarbon, evaporating HF `and 7 BFaY trom the remaining complexes at approximately atmospheric pressure in an evaporatng zone, withdrawing liquid from Athe evaporating zone to a decomposing zone,

decomposing remaining complexes in said last named zone vat reduced pressure, compressing HF and BFa from the evaporating zone and the decomposing zone and combin- -ing the compressed vapors with HF-BFa initially released from complexes leaving the reaction step, cooling the combined stream, pumping the liquid component of the cooled stream through a further cooler to the complexing zone, compressing a gasiform component of the cooled stream and passing the compressed material through a further cooler to the complexing zone, removing any residual HF and BFa from the liquid'stream from the decomposing zone and fractionating said stream to obtain substantially pure 1, i-dimethyl, S-ethyl benzene.

2. The process of claim 1 which includes the additional steps of washing at least a part of the liquid stream from the evaporating zone with a saturated hydrocarbon for separating liberated hydrocarbons from undecomposed complex in'said stream, and recycling at least a partof said liberated hydrocarbons to said complexing zone.

3. The process of claim 1 which includes the step of separating wash liquid from the liquid component of the cooled stream and returning said separated wash liquid to said washing zone.

4. The process of claim 1 wherein the uncomplexed hydrocarbons removed by washing include benzene and other uncomplexed hydrocarbons and which includes the step of recovering substantially pure benzene from other hydrocarbons thus removed from complex.

5. The process of claim 1 wherein the saturated hydrocarbon is pentane.

6. The method of producing benzene, meta-xylene and 1-,3-dimethyl, S-ethyl benzene which comprises complexing the aroma-tic components of a charging stock consisting -chiey of mixed xylenes and ethyl benzene in the ratio of about 1.6:1 to 5:1 and less than l0 percent of parainic and naphthenic hydrocarbons in the substantial absence of water with about 6 to 12 mols of HF and l mol of BFa per mol of total aromatic hydrocarbon in the charge in a complexing zone at a temperature of about 20 to 30 C. under a pressure of about 20 to about 50 p. s. i. g., pumping the resulting substantially homogeneous complex to a pressure of at least about 200 p. s. i. g. and heating i't to a temperature in the range of about 50 C. to about 70 C., said pressure being sufficient to maintain the HF in liquid phase at said temperature, maintaining the complex at said temperature and pressure for a period of about .4 to 4 hours, then reducing the pressure on reactionl products to remove liberated HF and BFs and to leave about 6 mols of HF and about 1 mol of BFa per mol of Cs and heavier aromatics in the product liquid, thereafter scrubbing the' product liquid with a wash liquid to remove substantially all aromatic hydrocarbons which are not complexed with HF and BFs, reducing the pressure on the Iscrubbed complex to approximately atmospheric pressurerand removing additional HF and BFa from the product liquid to etect liberation of at least a portion of complexed meta-xylene, thereafter stripping. product liquid at a pressure in Ithe range of l to 200 mm. at a temperature in the range of 100 C. to 150 C. to decompose remaining complex and liberate HF and BFs to the complexing step and fractionating the product liquid t-o recover substantially pure 1-,3-dimethyl, S-ethyl benzene.-

7. The method of claim 6 which includes the step of recycling liberated meta-xylene to the complexing zone in amount -suflicient to maintain a xylene to ethyl benzene ratio in said zone of at least about 3:1.

Y S. A process for converting the Cs aromatic components of a hydrocarbon charging stock consistingchiey `of mixed xylenes and ethyl benzene in the ratio of abou-t 1.611 to 5:1 substantially entirely into benzene, metaxylene and 1-,3dimethyl, S-ethyl benzene, which process comprises complexing the aromatic components of said'- Y8 charging stock in the absence of appreciable amounts of water with 6 t-o 12 mols of HFand A1 mol of BFs per mol of total aromaticv hydrocarbonrin the charge in a complexing zone maintained at a temperature of about 20Y C. 'to' 30"` C.. and a pressure of approximately 20 to 50 p. s. i. g., effecting substantially homogeneous phase conversion byreacting the resulting complex solution at a temperaturein Vthe range of C. to 70 C. fora period of about ,.4 to 4 hours under a pressure greater than the vapor pressure of hydrogen fluoride at said temperature, removing from ^the eflluent product stream HF and BF: liberated in the reaction zone to leave about 6 mols of HF and about. 1 mol of BF3 perV mol of Cs and heavier aromatics in the product liquid, then Washing in a wash zone the product liquid with about .2 to 2 volumes of saturated low lboiling hydrocarbon to remove substantially all hydrocarbons which Aare not complexed with HF and BFs, distillingsaid saturated low boiling hydrocarbon from the rich solution thus obtained and recy- Acling said saturated low boiling hydrocarbon to the washing step, fractionating the removed uncomplexed hydrocarbons t-o obtain substantially pure benzene, introducing Washed complex into an evaporator zone at approximately atmospheric pressure, heating said complex in the evaporator zone to liberate dissolved pentane and further amounts of HF and BFs, introducing liquid from the rst evaporating zone to a -second wash zone, Washing .lib-

y era-ted aromatics from said last named liquid inthe second Wash zone, passing washed .liquid from the second Wash zone to a decomposing zone operated at a pressure in the range of 10 mm. to 200 mm. absolute with a bottom temperature in the range of 100 C. to 150 C. todecomposeall remaining complex and liberate HF and BFS therefrom, compressing HFand BFS from the decomposing zone and from the evaporator zone to the pressure of HF and BF3 initially released from reactor eilluent and combining the streamsrof liberated HF and BFs, cooling the combined streams and separating them into a liquid and gaseous component, pumping at least a part of the liquid component through a cooler to ythe complexing n zone, compressing the gaseous component and introducing it through a cooler to the complexing zone, removing Y any residual HF and BF3 from hydrocarbons released in therdecomposing zone and fractionating said hydrocarbons to recover substantially pure meta-xylene and substantially pureY 1-,3-dimethyl, S-ethyl benzene respectively.

."9. The process of claim 8 Which includes the steps of y separating the'liquid component of the cooled combined streams of HF and BFs together with saturated low boiling hydrocarbon contained therein to obtain a liquid saturated low boiling hydrocarbonk stream and returning said last named stream to said wash zone.

' l0. A process for making 1-,3-dimethyl, S-'ethyl benzene from the Ca aromatic components of a hydrocarbon charging stock consisting chiefly of mixed xylenes and ethyl benzene' together with additional ethylene which "process comprises complexing the aromatic components temperatureinA the lrange of about 50 C. to 70 C. for

a period of about .4 to 4 hours under a pressure greater f Vthan thevapor'pressureof hydrogen fluoride at said temp'erature,4 introducing said additional ethylene into the homogeneous Vphase after said rcomplexing step .in such amounts that the mol percent of complexed 1,3,5-ethyl xylene formed in the reactor does not `exceed thermol percent vof xylenes therein, reducing the pressure on the reactionproducts to .remove liberated BFs and some HF and to leave about 6 mols ofl HF and about 1 mol of BFs per mol of-Cs andheavier aromatics Iin Ithe product liquid,

thereafter scrubbing the product liquid with a wash liquid torremove substantially all hydrocarbons which are not complexed withrHF and BF3,'reducing the pressure on 'the scrubbed complex solution, heating'said complex solu- 9 tion at said reduced pressure in an evaporator zone to liberate further amounts of HF and BFS, stripping liquid from the evaporator zone at reduced pressure and at a temperature in the range of about 100 C. to 150 C. to decompose any remaining complex and liberate further amounts of HF and BFS, recycling liberated HF and BFS to the complexing step, removing any residual HF and BFs from hydrocarbons withdrawn from 'the stripping zone and fractionating said hydrocarbons 'to recover substantially pure 1-,3-dimethyl, S-ethyl benzene.

References Cited in the tile of this patent UNITED STATES PATENTS Tuttle Nov. 19, 1935 Lien ct al. a Nov. 7, 1950 Lien et al. Aug. 19, 1951 Elwell Dec. 11, 1951 Lien et al. Dec. l, 1953

Claims (1)

1. A PROCESS FOR CONVERTING THE C8 AROMATIC COMPONENTS OF A HYDROCARBON CHARGING STOCK CONSISTING CHIEFLY OF MIXED XYLENES AND ETHYL BENZENE SUBSTANTIALLY ENTIRELY INTO BENZENE, META-XYLENE AND 1-, 3-DIMETHYL, 5-ETHYL BENZENE WHICH PROCESS COMPRISES COMPLEXING THE AROMATIC COMPONENTS OF SAID CHARGING STOCK IN SUBSTANTIALLY DRY STATE WITH AT LEAST ABOUT 6 MOLS OF HF AND 1 MOL OF BF3 PER MOL OF TOTAL AROMATIC HYDROCARBON IN THE CHARGE IN A COMPLEXING ZONE, INCREASING THE PRESSURE AND TEMPERATURE ON THE COMPLEXES THUS FORMED AND HOLDING COMPLEXES AT A TEMPERATURE IN THE RANGE OF ABOUT 50* C. TO ABOUT 70* C. UNDER A PRESSURE OF AT LEAST 200 P. S. I. G. AND HIGH ENOUGH TO INSURE LIQUID PHASE CONDITIONS LONG ENOUGH TO CONVERT SAID C8 AROMATIC HYDROCARBONS SUBSTANTIALLY ENTIRELY TO BENZENE, META-XYLENE AND 1-, 3-DIMETHYL, 5ETHYL BENZENE, REMOVING SUFFICIENT HF AND BF3 LIBERATED FROM COMPLEXES IN THE REACTION STEP TO LEAVE ABOUT 6 MOLS OF HF AND ABOUT 1 MOL OF BF3 PER MOL OF C8 AND HEAVIER AROMATIC HYDROCARBONS CONTAINED IN THE PRODUCT STREAM, THEREAFTER REMOVING UNCOMPLEXED HYDROCARBONS FROM THE COMPLEXES BY WASHING SAID COMPLEXES COUNTERCURRENTLY WITH A SATURATED HYDROCARBON, EVAPORATING HF AND BF3 FROM THE REMAINING COMPLEXES AT APPROXIMATELY ATMOSPHERIC PRESSURE IN AN EVAPORATING ZONE, WITHDRAWING LIQUID FROM THE EVAPORATING ZONE TO A DECOMPOSING ZONE, DECOMPOSING REMAINING COMPLEXES IN SAID LAST NAMED ZONE AT REDUCED PRESSURE, COMPRESSING HF AND BF3 FROM THE EVAPORATING ZONE AND THE DECOMPOSING ZONE AND COMBINING THE COMPRESSED VAPORS WITH HF AND BF3 INITIALLY RELEASED FROM COMPLEXES LEAVING THE REACTION STEP, COOLING THE COMBINED STREAM, PUMPING THE LIQUID COMPONENT OF THE COOLED STREAM THROUGH A FURTHER COOLER TO THE COMPLEXING ZONE, COMPRESSING A GASIFORM COMPONENT OF THE COOLED STREAM AND PASSING THE COMPRESSED MATERIAL THROUGH A FURTHER COOLER TO THE COMPLEXING ZONE, REMOVING ANY RESIDUAL HF AND BF3 FROM THE LIQUID STREAM FROM THE DECOMPOSNG ZONE AND FRACTIONATING SAID STREAM TO OBTAIN SUBSTANTIALLY PURE 1-, 3-DIMETHYL, 5-ETHYL BENZENE.

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